Permanent magnets as used, e.g., in relays, ringers, and electroacoustic transducers are made from materials which exhibit high values of magnetic coercivity, remanence, and energy product. Among alloys possessing such desirable properties are Al-Ni-Co-Fe, Mo-Co-Fe, and Co-Cr-Fe alloys, all of which comprise cobalt as an essential constituent. In view of the relatively high cost of cobalt, alloys are desirable in which cobalt plays no essential role; in this respect Mn-Al alloys are exemplary.
Mn-Al alloys have been extensively investigated and are the subject of a number of publications. For example, a metallographic study was made by H. Kono, "On the Ferromagnetic Phase in Manganese-Aluminum System", Journal of the Physical Society of Japan, Vol. 13, No. 12, December 1958, pp. 1444-1451. Acceptable magnetic properties have been achieved in Mn-Al alloys in at least two ways, namely, by inducing magnetic anisotropy or by the addition of carbon. Anisotropic Mn-Al magnetic alloys are disclosed by A. J. J. Koch et al., "New Material for Permanent Magnets on a Base of Mn and Al", Journal of Applied Physics, Supplement to Vol. 31, No. 5, May 1960, pp. 75S-77S; by Ya. S. Shur et al., "Influence of Plastic Deformation on the Magnetic Properties of a High-Coercivity Alloy Mn-Al", Fiz. Metal. Metalloved, Vol. 23, No. 2, pp. 338-339 (1967); and by R. A. McCurrie et al., "Dependence of the Permanent Magnet Properties of Mn.sub.55 Al.sub. 45 on Particle Size", IEEE Transactions on Magnetics, Vol. MAG-14, No. 5, September 1978, pp. 682-684. Mn-Al alloys comprising carbon are disclosed in U.S. Pat. No. 3,661,567, issued May 9, 1972 to H. Yamamoto; and alloys which not only comprise carbon but which are also magnetically anisotropic are disclosed by T. Ohtani et al., "Magnetic Properties of Mn-Al-C Permanent Magnet Alloys", IEEE Transactions on Magnetics, Vol. MAG-13, No. 5, September 1977, pp. 1328-1330.
Relevant with respect to the invention are techniques of rapid quenching of alloys as disclosed, e.g., by P. Duwez et al., "Rapid Quenching of Liquid Alloys", Transactions of the Metallurgical Society of AIME, Vol. 227, April 1963, pp. 362-365; by R. H. Willens et al., "Rapid Quenching of Reactive and Refractory Alloys from the Liquid State", Transactions of the Metallurgical Society of AIME, Vol. 236, February 1966, pp. 171-174; and by R. E. Maringer et al., "Casting of Metallic Filament and Fiber", Journal of Vacuum Science and Technology, Vol. 11, No. 6, November-December 1974, pp. 1067-1071.